Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 230637
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST TUE APR 22 2014

.SYNOPSIS...
STRONG RIDGING NORTH OF THE STATE WILL CONTINUE TO DRIVE BREEZY AND
GUSTY TRADE WINDS THROUGH FRIDAY. SHOWERS CARRIED BY THE TRADES WILL
CONTINUE TO BE FOCUSED MAINLY ALONG WINDWARD FACING SLOPES OF THE
ISLAND CHAIN...BUT SOME BRIEF SHOWERS WILL CONTINUE TO BE BLOWN OVER
TO LEEWARD SECTIONS OF THE SMALLER ISLANDS...ESPECIALLY DURING
NIGHTS AND MORNINGS. THERE MAY BE A SLIGHT INCREASE IN SHOWERS
ACROSS PARTS OF THE STATE ON THURSDAY. THE TRADE WIND SPEEDS ARE
EXPECTED TO GRADUALLY DECLINE FROM LATE SATURDAY INTO EARLY NEXT
WEEK.

&&

.DISCUSSION...
A 1029 MB SURFACE HIGH CENTERED NEAR 33N 142W...OR MORE THAN 1200
MILES NORTHEAST OF HONOLULU...IS MOVING TOWARD THE SOUTHEAST AT
ABOUT 10 MPH. A SURFACE RIDGE EXTENDS WEST SOUTHWEST FROM THIS HIGH
THROUGH A POINT ABOUT 625 MILES NORTH OF HONOLULU. THE RELATIVELY
TIGHT PRESSURE GRADIENT SOUTH OF THESE FEATURES CONTINUES TO
MAINTAIN BREEZY AND GUSTY TRADE WINDS ACROSS THE MAIN HAWAIIAN
ISLANDS EARLY THIS EVENING.

THE CLOSE PROXIMITY OF A STRONG MID-TROPOSPHERIC ANTICYCLONE
NORTHEAST OF THE ISLANDS IS MAINTAINING STABLE ATMOSPHERIC
CONDITIONS ACROSS THE REGION TONIGHT. AS A RESULT...THE LOW-LEVEL
TRADE WIND INVERSION WAS BELOW 4 THOUSAND FEET AT LIHUE IN THE EARLY
AFTERNOON SOUNDING...WHILE IT WAS ABOUT 7 THOUSAND FEET AT HILO AT
THE SAME TIME. THESE RELATIVELY LOW INVERSION HEIGHTS HAVE
CONTRIBUTED TO MAINTAINING THE GUSTY TRADE WINDS ACROSS PARTS OF THE
STATE TODAY. THIS IS ESPECIALLY TRUE IN VALLEYS DOWNWIND OF HIGHER
TERRAIN...SUCH AS THE KOOLAU MOUNTAIN RANGE. SATELLITE IMAGERY AND
RADAR REFLECTIVITY DATA ALSO SHOW LIMITED SHOWER BEARING CLOUDS OVER
AND UPSTREAM OF THE STATE. THEREFORE...THE STABLE CONDITIONS DUE TO
THE MID-TROPOSPHERIC ANTICYCLONE ARE LIKELY CONTRIBUTING TO THE
REDUCTION OF RAINFALL OVER MOST OF THE REGION. NOTE THAT AN UPPER
TROPOSPHERIC TROUGH NEAR KAUAI CONTINUES TO SEND PATCHES OF CIRRUS
MOVING UP OVER THE WESTERN END OF THE ISLAND CHAIN AT DUSK THIS
EVENING.

THE FORECAST MODELS INDICATE STRONG SURFACE RIDGING WILL CONTINUE
NORTH OF THE ISLANDS BETWEEN LATITUDES 30N AND 33N THROUGH FRIDAY.
THE TIGHT PRESSURE GRADIENT SOUTH OF THIS RIDGING WILL KEEP THE
TRADE WINDS BREEZY AND GUSTY. ALSO...THE STRONG MID-TROPOSPHERIC
RIDGING OVER THE REGION WILL MAINTAIN STABLE ATMOSPHERIC CONDITIONS
THROUGH THE END OF THE WORK WEEK. AT THE SAME TIME...THE LOW-LEVEL
TRADE WIND INVERSION WILL CAUSE PERIODS OF ENHANCED WIND GUSTS OVER
AND DOWNWIND OF HIGHER TERRAIN ACROSS PARTS OF THE STATE. IN
FACT...THE GFS AND ECMWF MODELS SUGGEST THERE MAY BE ANOTHER
INCREASE IN 850 MB WINDS BY LATE THURSDAY AT THE SAME TIME A NEW
SURFACE HIGH PASSES NORTH OF THE STATE. THIS COULD LEAD TO ANOTHER
ROUND OF STRONG TRADE WINDS...WHICH MAY REQUIRE THE ISSUANCE OF WIND
ADVISORIES FOR PARTS OF THE STATE.

IN REGARDS TO LOW CLOUDS AND PRECIPITATION...THE FORECAST GUIDANCE
INDICATES WE SHOULD CONTINUE TO HAVE A RATHER TYPICAL TRADE WIND
WEATHER PATTERN WITH LOW CLOUDS AND SHOWERS MAINLY AFFECTING
WINDWARD FACING SLOPES. HOWEVER...THE REMNANT MOISTURE FROM A
DECAYING FRONT EAST NORTHEAST OF THE STATE WILL LIKELY RIDE IN ON
THE INCREASING LOW-LEVEL TRADE WIND FLOW BY THURSDAY. AS A
RESULT...THERE MAY BE A SLIGHT INCREASE IN PRECIPITATION OVER
WINDWARD AND MAUKA AREAS THURSDAY. AT THE SAME TIME...THE
STRENGTHENING TRADE WINDS MAY CARRY SOME OF THESE SHOWERS OVER TO
LEEWARD SECTIONS OF SOME OF THE SMALLER ISLANDS...ESPECIALLY DURING
THE NIGHTS AND MORNINGS. BESIDES THE POTENTIALLY WETTER CONDITIONS
AROUND THURSDAY...THE FORECAST GUIDANCE DOES NOT SHOW ANY OTHER
ORGANIZED SYSTEM OF SHOWERS MOVING INTO THE AREA THROUGH THIS
WEEKEND.

IN REGARDS TO THE CIRRUS NEAR THE ISLANDS....THE UPPER LEVEL TROUGH
IS FORECAST TO CONTINUE TO WEAKEN AND LIFT OUT TO THE NORTHEAST.
HOWEVER...A NEW UPPER LEVEL TROUGH MOVING INTO THE AREA THIS WEEKEND
MAY PRODUCE HIGH CLOUDS AGAIN STARTING SATURDAY.

THE LONGER RANGE FORECAST MODELS INDICATE THE TRADE WIND SPEEDS WILL
BEGIN TO DECREASE FROM LATER THIS WEEKEND INTO EARLY NEXT WEEK AS
THE SURFACE RIDGE TO THE NORTH OF THE AREA WEAKENS. THE TRADE WIND
WEATHER PATTERN IS EXPECTED TO CONTINUE...WITH MAINLY WINDWARD AND
MAUKA SHOWERS. HOWEVER...A REMNANT FRONTAL BAND MAY MOVE SOUTHWARD
AND REACH THE STATE NEXT WEEK. BASED ON THE LATEST GUIDANCE...THIS
FEATURE MAY ENHANCE RAINFALL ACROSS PARTS OF THE STATE STARTING LATE
TUESDAY NIGHT OR WEDNESDAY.

&&

.AVIATION...
LOW CLOUDS AND SHOWERS CARRIED BY THE MODERATE TRADE WINDS WILL
AFFECT MAINLY WINDWARD AND MOUNTAIN AREAS...THOUGH WINDS ARE STRONG
ENOUGH FOR SOME OF THESE SHOWERS TO REACH LEE AREAS OF THE SMALLER
ISLANDS. VFR CONDITIONS WILL PREVAIL FOR ALL SITES...THOUGH PASSING
LOW CLOUDS AND SHOWERS MAY BRING BRIEF MVFR CEILING OR EVEN IFR
CEILING CONDITIONS MAINLY FOR THE WINDWARD SITES.

AIRMET TANGO FOR MECHANICAL TURBULENCE TO THE LEE OF MOUNTAINS
CONTINUES AT LEAST THROUGH EARLY WEDNESDAY MORNING DUE TO THE WINDS.

&&

.MARINE...
THE FRESH TO LOCALLY STRONG TRADE WINDS CONTINUE TO REQUIRE A SMALL
CRAFT ADVISORY /SCA/ REMAIN IN EFFECT FOR ALL HAWAIIAN CHANNELS AND
THE TYPICALLY WINDY WATERS ADJACENT TO THE BIG ISLAND AND MAUI.
SINCE THE TRADE WINDS WILL LIKELY REMAIN STRONG THROUGH THE
REMAINDER OF THE WORK WEEK...THE SCA IS CURRENTLY IN`EFFECT FOR
THESE WATERS THROUGH FRIDAY. NOTE THAT WE THERE MAY BE A SLIGHT
INCREASE IN WINDS ON THURSDAY...SO ADDITIONAL HAWAIIAN WATERS MAY
NEED TO BE ADDED TO THE SCA LATER THIS WEEK. THE FORECAST GUIDANCE
SUGGESTS THERE MAY BE A SLOW DECREASING TREND IN WINDS DURING THIS
WEEKEND AND EARLY NEXT WEEK...SO THE SCA MAY POSSIBLY BE DROPPED FOR
MOST OR ALL HAWAIIAN WATERS BY SUNDAY OR MONDAY.

THE ROUGH ELEVATED SURF CONTINUES JUST BELOW THE HIGH SURF ADVISORY
THRESHOLD ALONG EAST FACING SHORES. THE MOST RECENT OBSERVATIONS
FROM THE COASTAL BUOYS NEAR WINDWARD SHORES OF THE ISLANDS HAVE BEEN
SHOWING SIGNIFICANT WAVE HEIGHTS OF AROUND 8 FEET WITH A PERIOD 8 TO
9 SECONDS. THE WAVE WATCH III MODEL GUIDANCE SUGGESTS THERE WILL BE
LITTLE VARIATION IN THESE WAVE HEIGHTS AND PERIODS THROUGH FRIDAY.

ELSEWHERE...A NEW LONG-PERIOD NORTHWEST SWELL IS EXPECTED TO ARRIVE
WEDNESDAY...AND PEAK THURSDAY. THE WAVE WATCH III MODEL INDICATES
THE SWELL WILL REMAIN BELOW THE HIGH SURF ADVISORY CRITERIA ALONG
NORTH AND WEST FACING SHORES OF THE SMALLER ISLANDS. HOWEVER...WE
WILL MONITOR THE BUOY OBSERVATIONS ONCE THE SWELL ARRIVES IN CASE
THE SWELL IS LARGER THAN FORECAST. THIS NORTHWEST SWELL WILL
GRADUALLY SUBSIDE FROM FRIDAY THROUGH SATURDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR ALL HAWAIIAN
CHANNELS...MAALAEA BAY AND THE WATERS SOUTH OF THE BIG ISLAND.

&&

$$

DISCUSSION/MARINE...HOUSTON
AVIATION...HUI





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